The In the optical communication technology, particularly in a conventional optical MCM (Multi-Chip Module), a spatial multiplexing system which increases the number of channels is adopted in order to increase a signal band, and an array of light emitting elements for optical transmission such as a VCSEL (Vertical Cavity Surface Emitting Laser) of 12 channels and a 250 μm pitch and light receiving elements for optical reception, such as a PD (Photo Diode), is often used. While a VCSEL/PD chip is mounted on an optical waveguide of 12 channels, density is assumed to be increased to 24 channels and a 125 μm pitch, and 48 channels and a 62.5 μm pitch to widen a band further.
It is assumed that the optical waveguide is connected to an optical fiber. Therefore, when considering that a clad diameter of the optical fiber used in a present state is 125 μm, density increase has a limit of the 125 μm pitch. Even if the limit of 125 μm pitch is exceeded by reducing a diameter of the optical fiber, when a core width of a general multimode optical fiber being 35 μm and leakage of light are taken into consideration, the density increase of 48 channels or more is limited when the optical waveguide is one layer. Also, when the optical waveguide is turned to two or more layers, connection loss due to spread of a light beam becomes a serious problem.
FIG. 1 illustrates a schematic top plan view of a prior art optical module 100, whose density is increased by the conventional spatial multiplexing system. On a surface of a substrate 105, a plurality of optical waveguides 110 are disposed in high density. On one end of each optical waveguide 110, one light input/output part 115 which can be implemented by reflection means, like a mirror that is inclined at 45 degrees to reflect and change light from a horizontal direction to a vertical direction for instance, is provided separately without being arranged side-by-side; each light input/output part 115 includes two each of electric pads 120 for input and output, and a VCSEL/PD chip 125 is configured. When the optical waveguides 110 are arrayed with a 35 μm width and at a 62.5 μm pitch, a space between the optical waveguides 110 is 27.5 μm. Considering the leakage of the light, it is difficult to implement electric wiring from the electric pads 120 so as not to exert an influence on the array of the optical waveguides 110.
One known technology involves a 500-Gbps parallel wavelength division multiplexing (PWDM: Parallel Wavelength Division Multiplexing) optical interconnect for executing 48-channel data transmission of 10.42 Gbps by 12 optical fiber ribbons in parallel having four wavelengths per optical fiber. While rough wavelength multiplexing is used to connect the VCSEL, the PD, and the optical fiber in order to increase the density, propagation of light is controlled only by reflection in the optical interconnect; there is no structure which controls the propagation of the light by a waveguide, and insertion loss (loss from light reception or emission to the optical fibers coupling) is as large as 6-8 dB in each of a transmitter and a receiver.
Another known technology involves applying an optical pin having a mirror surface inclined at 45 degrees to carry out 90-degree optical path conversion at a distal end to an optical waveguide and optically coupling a VCSEL or a PD disposed on the optical waveguide and the optical waveguide. In the optical communication technology, since one VCSEL or PD is provided in correspondence in one optical waveguide, and only one optical signal corresponding to the VCSEL or PD is transmitted and received in one optical waveguide, this optical communication technology is not different from the conventional spatial multiplexing system.
Another known technology involves providing an optical path conversion mirror inclined at 45 degrees in an optical waveguide inside a substrate and optically coupling a light emitting element or a light receiving element disposed on the substrate and the optical waveguide. Also in this optical communication technology, since one light emitting element or light receiving element is provided in correspondence in one optical waveguide, and only one optical signal corresponding to the light emitting element or the light receiving element is transmitted and received in one optical waveguide, this optical communication technology is not different from the conventional spatial multiplexing system either.
Another known technology involves an optical receiver wherein a first substrate that is formed of a light transmissive material and has a plurality of light receiving elements formed on a front surface and a plurality of V grooves formed on a back surface, and a second substrate that is formed of a light transmissive material of the same refractive index as the first substrate and has a plurality of projections in a shape to be fitted with the V grooves formed on a front surface, are integrally molded by being joined by fitting the V grooves and the projections respectively. Wavelength multiplexed light that passes through crossing the fitted V grooves and projections pass through without being reflected on a non-reflection film formed on one slant face of each V groove, and only the light of a corresponding wavelength is reflected at a band rejection filter formed on the other slant face of each V groove, passes through the first substrate and enters the light receiving element. While the light is propagated through the first substrate and the second substrate, the light is reflected as it is since one interface of each V groove is a 45-degree slant face, so that it is needed to form the non-reflection film on the slant face in order to propagate the light. Also, since there is no structure of confining the propagation of the light by a waveguide, insertion loss becomes large.